Each time Paul Volker delivers one of his interim reports, the United Nations receives another body blow and its tarnished reputation suffers yet again.

This was the third of Mr Volcker's reports and in many ways the most damning yet.

Until now there was the strong whiff of scandal, but no direct blame.

This report, though, pointed the finger straight at the former head of the oil-for-food programme, Benon Sevan.

It concluded that Mr Sevan "corruptly benefited" from his role with the UN - that he had received kickbacks worth almost $150,000 from a small company called Amep, who he had helped profit from the sale of Iraqi oil.

Mr Sevan denies the allegation and insists he received that money from his aunt.

But the investigators believe they have joined up all the dots and now have called on Kofi Annan to lift his diplomatic immunity to allow a prosecution to take place.

Not over yet

It is not just one man.

A former UN official, Alexander Yakovlev, is now being held in custody and has pleaded guilty to accepting hundreds of thousands of dollars in bribes from UN contractors.

The UN Secretary General agreed to lift his immunity following a request from a New York District Attorney's office.

Iraq's oil is one of its most important resources

And its not over yet.

The tentacles of this investigation continue to reach much wider. What of the private companies involved?

But perhaps most importantly, there are the fresh questions about Kofi Annan himself.

Just a few months ago, following the publication of the second report, it looked like he was in the clear.

His son, Kojo, had been paid as an adviser to a Swiss based company called Cotecna, which successfully bid for a contract in the lucrative oil-for-food programme.

The earlier report concluded that while there were "significant questions" about the integrity of Kojo Annan - the sins of son could not be visited on the father.

More suspicion

But since then, an e-mail has emerged which raises more questions about Kofi Annan and his dealings with Cotecna.

Mr Volcker believes it demands further investigation, and once again Mr Annan is under suspicion.

Kofi Annan is not wholly clear of suspicion

Kofi Annan's spokesman, Mark Malloch Brown, says that Mr Annan is disappointed with that decision and it is easy to see why.

Next month, the world's leaders will attend a summit in New York to discuss United Nations reform - at about the same time as Paul Volcker will deliver his next report.

Mr Annan, who will be the host, is still uncertain as to the scale of damage to his own reputation and the organisation he leads.

Not quite the circumstances in which he would have wanted to lead this debate.

But maybe just the kind of environment for some countries that have been highly critical of the UN to argue for fundamental change.